Weep Screeds and Halloween

There actually is a connection between the most commonly used weep screeds and Halloween — they both can involve some scary outcomes!  The purpose of a weep screed in thin veneer wall is to provide drainage at the bottom of the thin veneer wall. Unfortunately, the manufacturer’s literature often states that this drainage space will come from the formation of a shrinkage crack. This is neither a predictable nor adequate solution for providing the necessary drainage of moisture at the bottom of a thin veneer wall.

A paradigm shift is needed when it comes to draining thin veneer walls. Most architects and builders now recognize the need for a drainage plane (commonly referred to in the industry as a drainage mat) behind thin veneers. These products create a space behind the veneer that acts as a capillary break and a transport mechanism to move water that gets into the building envelope down to the bottom of the wall. The problem arises when that moisture reaches the base of the wall; the most commonly employed weep screeds restrict the flow out of the wall because of that pesky shrinkage crack! And no, those tiny little holes are not for drainage. Again citing the manufacturer’s literature, they are for “attachment purposes (not weeping).

Moisture-related failure of walls is not as much about volume of water in walls as it is about the time that some moisture is allowed to remain in that wall. If an adequate opening isn’t available at the bottom of the wall for moisture to exit and adequate airflow to occur, the wall is ripe for failure.

I prefer to remain optimistic about the building industry, but I recently read an article in a national building trades publication on the correct installation of adhered masonry veneers that set my optimism back a bit. As many of you know, adhered concrete masonry veneers have experienced a large number of moisture-related issues when not installed properly. Many articles have been written about this issue including “Best Practices: Adhered Concrete Masonry Veneer” by Mark Parlee that appeared in the Journal of Light Construction. Parlee, who is a builder as well as a forensics expert, notes in his article that ACMV walls have now become a trigger for inspections because of the large number of moisture-related failures they have experienced. He goes on to state that the solution is “drainage.”

Back to the article I read. It implied that drainage was necessary, but it referenced the use of two layers of WRB to create that drainage. That is a very old technique, proven by testing to retard the rapid transport of moisture out of walls. It does not provide the minimum drainage space specified by respected scientists like Dr. Joseph Lstiburek. In his article Mind the Gap, Eh! a minimum 1/8” gap or void needs to be present to create a capillary break and an effective drainage mechanism.

The building trades magazine article also mentioned the use of a weep screed, but it did not indicate what to look for in an effective product. Remember, the holes are for attachment, and a shrinkage crack isn’t predictable. I am disappointed that while we seem to embrace the goal of better buildings, we still employ old, outdated techniques even though many of the new materials we build with don’t work with the old way of doing things.  We need that paradigm shift!

You need to look for a weep screed that provides frequent, large openings for drainage. They do exist. Without “real” drainage space behind the veneer and “real” openings at the bottom of walls, you will wind up with a moisture “trick” rather than the “treat” of a beautiful, long-lasting building. Happy Halloween, hope you get a treat!

*For more information about weep screeds and weeps at the bottom of walls, download the MTI article “MTI-014: Getting to the Bottom of Moisture Management” in the MTI Library at http://www.MTIdry.com.

ACMV wall failure in a Midwest hotel.

This photo shows a moisture-related ACMV wall failure in a Midwest hotel.

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Creating Sustainable Rainscreen Building Envelopes: It’s Like Motorcycles and Rain Suits!

Sustainable building isn’t possible without moisture management.  And for those forced to live or work in a building without moisture management, life becomes a health and safety nightmare.  Bold statements, but totally supportable.

According to the HUD’s Path Project, “Moisture, in all of its physical forms, is commonly regarded as the single greatest threat to durability and the long-term performance of the housing stock.  Excessive exposure to moisture is not only a common cause of significant damage to many types of building components and materials, it also can lead to unhealthy indoor living environments.  A long list of serious adverse effects can result from moisture problems in houses.  There is wide agreement that successful management of moisture in its various forms is essential for houses (buildings) to be durable, safe and energy efficient.”  In its 2004 report, the Path Projected listed the following outcomes of uncontrolled moisture in the building envelope:

  • Decay of wood and corrosion of metals
  • Infestation by termites and other destructive insects
  • Negative impacts on indoor air quality
  • Growth of mold, mildew and other biological contaminants
  • Reduced building material strength
  • Expansion/contraction damage to materials
  • Reduced thermal resistance of wet insulation
  • Premature failures of paints and coatings
  • Damage to building contents
  • Negative effects on building aesthetics

Enter the key phrase sustainable rainscreen building envelope into Google and you will get more than 18,000 results, including MTI’s “Drainable is Sustainable” presentation delivered at last fall’s technical meeting of the Sealant Waterproofing and Restoration Institute.  A key point of the presentation is that a moisture management solution for the rainscreen building envelope requires a systemic/holistic approach.  There is no single magic bullet; it takes a well-thought-out, coordinated system of products and processes designed and implemented by a team of professionals working collaboratively at every stage of the project to reach a successful outcome.

To illustrate the importance of a coordinated system in moisture management, I used the analogy of a motorcyclist riding towards an approaching storm in that presentation.

“It’s a nice sunny day, so I decide to go for a motorcycle ride.  Being an experienced motorcyclist, I always have raingear in my saddlebags because it’s summer and anything is possible!  As I move through the countryside, I notice that the sky is darkening and a storm is imminent so I pull over and put on my rain suit.

In a matter of minutes, the rain starts.  It’s light at first but soon becomes heavy, and it’s coupled with a driving wind.  Rain is forced around my windshield and into my eyes greatly limiting my ability to see the road.  Water cascades off my helmet and runs down the back of my neck soaking my shirt.  The water on the highway flies upward leaking into my boots through the seams and around the tongue.  To make matters even worse, it’s a hot, humid day so beads of condensation start to form on the inside of my rain suit making for an increasingly miserable ride!  Obviously, even though I thought I was prepared for rain, I hadn’t looked at all possibilities.”

Even though I had a collection of items designed to keep me dry, I hadn’t thought out the outcome fully, and I hadn’t properly combined the items into a functioning system.  If I had used goggles or a helmet with a visor, I could have seen the road better.  If I had used the hood on my jacket and worn it under the helmet, I wouldn’t have gotten rain down my back.  If I had used a rain jacket with vents, air could have moved around inside the system and reduced the condensation. Finally, had I worn rain boots with my rain pants lapped over the top of the boots and fastened snugly, I wouldn’t have got wet from the water spraying up from the road.

So what can be learned from this analogy about the importance of a system in solving the building envelope moisture management problem?  It takes many products, put on in the right order and at the right time, to create a positive result. We need to look at how many factors are in play and then employ several moisture management solutions as part of a system to solve the problem.

This same idea of a coordinated, multi-component solution can be applied to the people designing, specifying and constructing a building.  Gone are the days when designers, specifiers and contractors could successfully do their jobs in a vacuum.  There are just too many new products, processes and complex codes for the “Lone Ranger” approach to work.  Everyone must collaborate and communicate if a sustainable, healthy building is the goal.

Those are my thoughts; I welcome yours!

HD Big Twin